Prof Patrick Roche

Abstract:

Aliphatic hydrocarbons exhibit an absorption feature at 3.4 μm, observed toward sources that sample diffuse regions of the interstellar medium (ISM). The absorbers responsible for this feature are assumed to reside in some component of interstellar dust, but the physical nature of the particles (size, shape, structure, etc.) is uncertain. Observations of interstellar polarization provide discrimination. Since the grains that carry the silicate absorption feature are known to be aligned, polarization across the 3.4 μm hydrocarbon feature can be used to test the silicate-core organic refractory mantle grain theory. Although the 3.4 μm feature has been observed to be devoid of polarization for one line of sight toward the Galactic center, a corresponding silicate polarization measurement for the same line of sight was not available. Here, we present spectropolarimetric observations of GCS 3-11 and GCS 3-IV toward the Galactic center, where the 9.7 μm silicate polarization has been previously observed. We show that polarization is not detected across the 3.4 μm feature to a limit of 0.06% ± 0.13% (GCS 3-II) and 0.15% ± 0.31% (GCS 3-IV), well below the lowest available prediction of polarization on the basis of the core-mantle model. We conclude that the hydrocarbons in the diffuse ISM do not reside on the same grains as the silicates, and likely form a separate population of small grains. © 2006. The American Astronomical Society. All rights reserved.

Abstract:

We report the results of near infrared spectroscopy of 11 luminosity-selected candidate planetary mass objects (PMOs) in the Trapezium Cluster with Gemini South/Gemini Near-Infrared Spectrograph and Gemini North/Near-Infrared Imager. Six have spectral types ≥M9, in agreement with expectations for PMOs. Two have slightly earlier types, and three are much earlier types which are probably field stars. Four of the six sources with types ≥M9 have pseudo-continuum profiles which confirm them as low gravity cluster members. The gravity status of the other cool dwarfs is less clear but these remain candidate PMOs. The derived number fraction of PMOs with M = 3 - 15 MJup is 1-14 per cent, these broad limits reflecting the uncertainty in source ages. However, the number fraction with M < 20 MJup is at least 5 per cent. These detections add significantly to the body of evidence that a planetary mass population is produced by the star formation process. © 2006 The Authors. Journal compilation © 2006 RAS.

Abstract:

We present high spatial resolution radio and near-infrared hydrogen recombination line observations of the southern massive star forming region G333.6-0.2. The 3.4-cm continuum peak is found slightly offset from the infrared (IR) source. The H90α spectra show for the first time a double-peak profile at some positions. The complex velocity structure may be accounted for by champagne outflows, which may also explain the offset between the radio and IR sources. The 2.17-μm Brγ image and H90α map are combined to construct an extinction map which shows a trend probably set by the blister nature of the H ii region. The total number of Lyman continuum photons in the central 50-arcsec is estimated to be equivalent to that emitted by up to 19 O7V stars. © 2006 RAS.